Radiance-general Digest, Vol 59, Issue 8

Hi Galen,

No problem.

Regarding the header

    * Rc<r,g,b> - these are the rgb components for the reflectance on
      the "coated" side of the monolithic glass
    * Rg<r,g,b> - these are the rgb components for the reflectance on
      the non-coated side of the monolithic glass
    * T<r,g,b> - these are the rgb components for the transmittance for
      the monolithic glass
    * Part - this is a boolean value
          o 0 means this is a regular glass
          o 1 means this is a frit - if this is the case the "coated"
            side reflectance needs to represent the reflectance of the
            frit at 100% coverage which should be possible to extract
            from the glazing manufacturer

The RGB values are extracted from the file generated for a "radiance" export from Optics. This should be for a single pane monolithic glass description (not a multi-layer make-up). The file will have three Radiance material definitions, the two BRDTfunc definitions are the ones to pay attention to. The makeup is something like the following:

    void BRTDfunc some.glass.front
    10

        Rfr Rfg Rfb
        Tr Tg Tb
        0 0 0
        .

    9 0 0 0 0 0 0 0 0 0

    void BRTDfunc some.glass.back
    10

        Rbr Rbg Rbb
        Tr Tg Tb
        0 0 0
        .

    9 0 0 0 0 0 0 0 0 0

So you need to take the two rgb triples for reflectance and one for transmittance. So an entry in the data file could look like this (you will need to figure which represents the coated side if needed):

    Surface Tr Tg Tb Rcr Rcg Rcb Rgr Rgg Rgb Part
    <name> Tr Tg Tb Rfr Rfg Rfb Rbr Rbg Rbb 0
      
A file for a double pane insulating unit might look like the following:

    Surface Tr Tg Tb Rcr Rcg Rcb Rgr Rgg Rgb Part
    green-lowe Tr Tg Tb Rfr Rfg Rfb Rbr Rbg Rbb 0
      
The glaze script contains a default "clear" glass. I seem to recall that this is required for the script to output a material description (eg it must have a "clear" glass description"). If this is not suitable the script requires some modification, which I think I can offer some guidance on so that you can include your own "clear" glass description.

I would suggest before you do anything else you should test out the script as is with the built in values. This will let you see how it works. You will assign different materials to different layers to build up the composite unit.

Try it out and let me know if you have more questions.

-Jack

Galen Burrell wrote:

···

Jack,
Thanks for the input and offer to answer a few questions. Much appreciated.
I see the header information the glaze script is looking for the following when importing a data file:

Surface Tr Tg Tb Rcr Rcg Rcb Rgr Rgg Rgb Part

Questions:
1. Are the RGB values for T, Rc, Rg easily found in Optics 5? I selected 'Color - Transmittance' under Tools>Select Spectrum, and tried all the different wavelength functions, but I'm not seeing RGB anywhere.
Am I missing something?
2. Between Rc and Rg, which one refers to outside surface?
3. What does 'Part' refer to in the header above?
4. For a double pane IGU with a low-e coating on green glass (surface 2), would the data file look something like this?

Surface Tr Tg Tb Rcr Rcg Rcb Rgr Rgg Rgb Part
1 Trgb, Rrgb, Part information for green glass
2 Trgb, Rrgb, Part information for green glass + LowE coating (or would it be just the LowE coating?)
3 Trgb, Rrgb, Part information for clear glass
4 Trgb, Rrgb, Part information for clear glass

Thanks for your time and assistance - much appreciated.

Galen

Message: 3
Date: Wed, 14 Jan 2009 18:08:02 -0500
From: Jack de Valpine <[email protected]>
Subject: Re: [Radiance-general] Glazing transparency/reflectivity
        study
To: Radiance general discussion <[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset="iso-8859-1"

Hi Galen,

You should probably consider the glaze script to produce a material
description for your glazing. I think that this will you get the most
sophisticated description for a glass material. You can incorporate data
that is output from Optics for single monolithic glass types to build up
double pane insulating units if needed. A coating can be applied to a
selected layer of the make-up. Note, that using the simple BRTDfunc
description output from Optics (unless this has been updated in the past
few years) does not account for variation due to incident angle. There
is actually a way to set up the glaze script so it accepts a file of
glass types as input rather than using the rather minimal inputs that
come with script.

Let me know if you have any questions and I will do the best I can to
help out.

-Jack

Galen Burrell wrote:
  

I'm considering doing a study comparing the transparency (as viewed
from outside) of two glazing types on a building modeled in
radiance. The study would render several viewpoints (and view angles
looking up the facade) for the multiple glass types under a variety of
sky conditions (sunny, cloudy, etc). The primary goal of the study
would be to as follows:

1. Demonstrate how exterior transparency changes with different glass
types (with different coatings and exterior reflectances)
2. Demonstrate how exterior transparency changes with angle of incidence
3. Demonstrate how exterior transparency changes based on ratio of
interior to exterior illuminance (or more accurately, luminances).

I'm only interested in this as a comparative study: does glass type A
look clearer than glass type B when viewed at X angle and under Y sky
condition, and Z interior/exterior illuminance ratio.

My question to the list is:
1. Comments on the usefulness of this study?
2. Advantage of using Optics 5 rad file (BRTDfunc) over glass
primitive? My understanding is it more accurately captures the color
of the glass and reflectivity... anything else?

Thanks,
Galen

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# visarc incorporated
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# channeling technology for superior design and construction